TMultiCast is a record type that represents internet address structures used when manipulating socket options for TIdIPMCastClient and TIdIPMCastServer. TMultiCast is used with API- or OS-level calls that join or depart a multicast group, and when data is sent to the multicast group address. 

IMRMultiAddr is a TIdInAddr member that represents the native internet address structure for the multicast group address. 

IMRInterface is a TIdInAddr member that represents the native internet address structure for the local IP address used for datagram transmission and/or receipt.

TIdIPMCastClient.Bindings TIdIPMCastServer